Moving object, wireless power feeding system, and wireless power feeding method

ABSTRACT

An object is to provide a moving object structure capable of reducing power loss caused when power is supplied from a power feeding device to a moving object by wireless communication. Another object is to provide a moving object structure capable of reducing the strength of a radio wave radiated to the surroundings. Before power is supplied to a moving object, a radio wave for alignment of antennas is output from a power feeding device. That is, radio waves are output from a power feeding device in two stages. In a first stage, a radio wave is output to align positions of antennas of the power feeding device and the moving object. In a second stage, a radio wave is output to supply power from the power feeding device to the moving object.

This application is a continuation of U.S. application Ser. No.13/018,791 filed on Feb. 1, 2011 which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a moving object which is driven by anelectric motor and includes a secondary battery chargeable by wirelesscommunication. The present invention also relates to a wireless powerfeeding system including a moving object and a power feeding devicewhich supplies power to the moving object through wirelesscommunication. The present invention further relates to a wirelesscommunication method for use in the wireless power feeding system.

2. Description of the Related Art

In recent years, energy saving, creation and storage technologies areattracting more attention because environmental problems such as globalwarming are becoming more severe. In the case of a moving object with asecondary battery, i.e., a moving object which is driven by an electricmotor using power provided from a secondary battery, including but notlimited to a two-wheeled vehicle or a four-wheeled vehicle such as abicycle having a motor and an electric car, energy storage techniquesare used and in addition, an amount of carbon dioxide emissions can bereduced. Therefore, techniques used for such a moving object are beingdeveloped actively.

At present, the secondary battery of the moving object can be charged byusing a general home AC power source as a power feeding device or byusing a public power feeding facility having a power feeding device suchas a high-speed battery charger. In either case, a connector which makeselectric connection by insertion of a plug into a socket is commonlyused.

For charging of a secondary battery using such connection with the useof a connector, an electric connection between a moving object and apower feeding device is made by bringing a conductor of a plug intocontact with a conductor of a socket. This requires plugging-in/outoperations for every charging, which may deteriorate the connector dueto repeated charging operations. In addition, a large-sized movingobject such as an electric car requires high power for charging. Thismay raise safety issues since damage from an electric shock or a shortcircuit due to moisture or the like may be significant. Accordingly,special care is needed for handling the connector in the moving object.

In order to avoid the above problems associated with a connector,research and development are being conducted to propose a wireless powerfeeding system for supplying power from a power feeding device to amoving object by wireless communication (for example, see PatentDocument 1). Use of such a wireless power feeding system allows asecondary battery to be charged without using any connector.

REFERENCE

[Patent Document 1] Japanese Published Patent Application No.2004-229425

SUMMARY OF THE INVENTION

In the above-described wireless power feeding system, a radio wavetransmitted from an antenna of the power feeding device is received byan antenna of the moving object. The received radio wave is convertedinto electric energy, which is then stored in the secondary battery. Theefficiency of converting energy of the radio wave into electric energydepends on a positional relationship between the antenna of the powerfeeding device and the antenna of the moving feeding device. That is,misalignment between the positions of the power feeding device and theantenna of the moving object leads to a low conversion efficiency, whichresults in inefficient charging of the secondary battery. However, it isdifficult in most instances for a driver of the moving object torecognize the positional relationship between the antennas of the movingobject and the power feeding device while driving the moving object,although it depends on where the antennas are installed.

In addition, in many cases, the antenna of the power feeding deviceoutputs a substantially constant high power radio wave. Thus, if theconversion efficiency for charging is low due to misalignment betweenthe antennas, power may be dissipated and a high power radio wave whichhas not been converted into electric energy may be radiated to thesurroundings. Although it is known that irradiation of the radiatedradio wave on a living body such as a human body causes no problem sincemost of the radiated radio wave is absorbed into the body and is changedinto heat, an effect of a radio wave on a living body has not yet beencompletely explained. Therefore, it is desirable to reduce the strengthof the radio wave radiated to the surroundings.

In consideration of the above problems, an object of the presentinvention is to provide a structure of a moving body which enablesreduction of power loss caused when power is supplied from a powerfeeding device to a moving object by wireless communication. Anotherobject of the present invention is to provide a structure of a movingbody which enables reduction of the strength of a radio wave radiated tothe surroundings.

Another object of the present invention is to provide a wireless powerfeeding system and a wireless power feeding method which enablereduction of power loss when power is supplied from a power feedingdevice to a moving object by wireless communication. Another object ofthe present invention is to provide a wireless power feeding system anda wireless power feeding method which enable reduction in strength of aradio wave, which is radiated from a power feeding device to thesurroundings during a charging operation.

In order to solve the above problems, according to one embodiment of thepresent invention, before power is supplied to a moving object, a radiowave for alignment of antennas is output from a power feeding device.That is, a radio wave is output from a power feeding device in twostages. In a first stage, a radio wave is output to align the positionsof the antennas of the power feeding device and the moving object. In asecond stage, a radio wave is output to supply power from the powerfeeding device to the moving object.

When the radio wave in the first stage is output from the power feedingdevice, the moving object receives the radio wave and converts it intoan electric signal. Strength of the electric signal includes data on apositional relationship in distance, direction, or the like between theantenna of the power feeding device and the antenna of the movingobject. Thus, the electric signal is used to detect the positionalrelationship between the antennas. Accordingly, the position ordirection of the moving object or the power feeding device can bemodified to provide the optimal positional relationship for the supplyof power.

In addition, the strength of the radio wave which is output in the firststage may be sufficient as long as the positional relationship betweenthe antenna of the power feeding device and the antenna of the movingobject can be detected. Accordingly, the strength of the radio wavewhich is output in the first stage can be lower than strength of theradio wave for supply of power into the moving object, which is outputin the second stage.

As used herein, the term “moving object” means something driven by anelectric motor using power stored in a secondary battery and includes,for example, automobiles (automatic two-wheeled cars, three ormore-wheeled automobiles), motorized bicycles including a motor-assistedbicycle, aircrafts, boats, and railroad cars.

Specifically, according to one embodiment of the present invention, amoving object includes an antenna circuit which generates a firstelectric signal and a second electric signal from a first radio wave anda second radio wave sequentially transmitted from a power feedingdevice, respectively; a signal processing circuit which extracts data ona positional relationship between the power feeding device and themoving object, using the first electric signal; a secondary batterywhich stores electric energy using the second electric signal; and anelectric motor into which electric energy from the secondary battery issupplied.

In addition, according to one embodiment of the present invention, awireless power feeding system includes a power feeding device includinga first antenna circuit; and a moving object. The moving object includesa second antenna circuit which generates a first electric signal and asecond electric signal from a first radio wave and a second radio wavesequentially transmitted from the first antenna circuit, respectively; asignal processing circuit which extracts data on a positionalrelationship between the moving object and the power feeding device,using the first electric signal; a secondary battery which storeselectric energy using the second electric signal; and an electric motorinto which electric energy from the secondary battery is supplied.

In addition, according to one embodiment of the present invention, awireless power feeding method includes transmitting a first radio wavefrom a first antenna circuit of a power feeding device; generating afirst electric signal from the first radio wave in a second antennacircuit of a moving object; extracting data on a positional relationshipbetween the power feeding device and the moving object, using the firstelectric signal in a signal processing circuit of the moving object, inorder to determine whether or not a second radio wave is transmittedfrom the first antenna circuit based on the positional relationship;generating a second electric signal from the second radio wave in thesecond antenna circuit if the second radio wave is transmitted from thefirst antenna circuit; storing electric energy in a secondary battery ofthe moving object, using the second electric signal; and supplying theelectric energy from the secondary battery to an electric motor of themoving object.

In addition, a driver of the moving object or a controller of operationof the power feeding device may manually determine whether to startcharging the secondary battery based on data on the positionalrelationship between the power feeding device and the moving object,which is extracted by the signal processing circuit. Alternatively, thesignal processing circuit of the moving object may determine whether tostart charging of the secondary battery and transmit a result of thedetermination, as a radio wave signal, to the power feeding device.Alternatively, the data on the positional relationship between the powerfeeding device and the moving object may be, as it is, transmitted, as aradio wave signal, from the moving object to the power feeding device inwhich it may be then determined whether to start the charging of thesecondary battery.

According to one embodiment of the present invention, the positionalrelationship between the antenna of the power feeding device and theantenna of the moving object can be easily optimized, which may resultin reduction of power loss which may be caused when the battery ischarged. In addition, it is possible to reduce the strength of a radiowave radiated to the surroundings from the power feeding device withoutbeing used for charging.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing configurations of a moving object and awireless power feeding system.

FIG. 2 is a view showing configurations of a moving object and awireless power feeding system.

FIG. 3 is a flow chart showing operations of a moving object and a powerfeeding device.

FIG. 4 is a flow chart showing operations of a moving object and a powerfeeding device.

FIG. 5 is a view showing configurations of a moving object and awireless power feeding system.

FIG. 6 is a view showing configurations of a moving object and awireless power feeding system.

FIG. 7 is a view showing configurations of a moving object and awireless power feeding system.

FIGS. 8A to 8C are views showing states where a moving object approachesa power feeding device antenna circuit.

FIGS. 9A and 9B are view showing states where a power feeding deviceantenna is adjacent to a moving object antenna.

FIGS. 10A and 10B are circuit diagrams of antenna circuits.

FIGS. 11A to 11C are views each showing a shape of an antenna.

FIGS. 12A and 12B are views showing a power feeding device and a movingobject.

FIGS. 13A and 13B are views each showing a moving object.

FIGS. 14A and 14B are circuit diagrams of rectifier circuits.

FIGS. 15A to 15D are views showing structures of transistors.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings. However, it shouldbe understood to those skilled in the art that the present invention isnot limited to the following description and various modifications andchanges may be made without departing from the spirit and scope of theinvention. Therefore, the present invention should not be construed asbeing limited to the disclosed embodiments.

Embodiment 1

A configuration of a moving object and a wireless power feeding systemusing the moving object and a power feeding device according to oneembodiment of the present invention are shown in a block diagram of FIG.1 by way of an example. Although the block diagram shows separateelements within the moving object or the power feeding device accordingto their functions, as independent blocks, it may be practicallydifficult to completely separate the elements according to theirfunctions and, in some cases, one element may involve a plurality offunctions.

As shown in FIG. 1, a moving object 100 includes a power receivingdevice portion 101 and a power load portion 110. The power receivingdevice portion 101 includes at least a moving object antenna circuit102, a signal processing circuit 103, and a secondary battery 104. Inaddition, the power load portion 110 includes at least an electric motor111.

In addition, the secondary battery 104 is a charge storage means.Examples of the charge storage means include a lead-acid battery, anickel-cadmium battery, a nickel-hydride battery, and a lithium-ionbattery.

In addition, a power feeding device 200 includes a power feeding deviceantenna circuit 201 and a signal processing circuit 202. The signalprocessing circuit 202 controls operation of the power feeding deviceantenna circuit 201. That is, the signal processing circuit 202 cancontrol the strength, the frequency, and the like of radio wavestransmitted from the power feeding device antenna circuit 201.

The power feeding device 200 transmits an alignment radio wave as a testsignal from the power feeding device antenna circuit 201 in order toalign the moving object 100 and the power feeding device 200 beforesupplying power to the moving object 100. The moving object 100 receivesthe test signal in the moving object antenna circuit 102, converts itinto an electric signal, and then transmits the electric signal to thesignal processing circuit 103.

The strength of the received test signal depends on a positionalrelationship in distance, direction, or the like between the movingobject antenna circuit 102 and the power feeding device antenna circuit201. The signal processing circuit 103 extracts data on the positionalrelationship between the moving object antenna circuit 102 and the powerfeeding device antenna circuit 201 from the strength of the receivedtest signal.

If the strength of the received test signal is sufficiently high, itmeans that an efficiency of energy conversion in converting the radiowave into the electric signal is sufficiently high. Accordingly, thepositional relationship between the moving object antenna circuit 102and the power feeding device antenna circuit 201 is determined to be ina state adapted to start of charging.

On the contrary, if the strength of the received test signal isinsufficient, it means that an efficiency of energy conversion inconverting the radio wave into the electric signal is low. Accordingly,the positional relationship between the moving object antenna circuit102 and the power feeding device antenna circuit 201 is determined to benot in a state adapted to start of charging.

The criterion for determining whether or not the positional relationshipbetween the moving object antenna circuit 102 and the power feedingdevice antenna circuit 201 is in a state adapted to start of chargingmay be properly set by a designer.

In addition, a driver of the moving object 100 or a controller ofoperation of the power feeding device 200 may manually determine whetherto start charging of the secondary battery 104 based on data on thepositional relationship extracted by the signal processing circuit 103.

The charging of the secondary battery 104 is performed by transmitting acharging radio wave from the power feeding device antenna circuit 201 ofthe power feeding device 200. In the moving object 100, the chargingradio wave is received in the moving object antenna circuit 102 andconverted into an electric signal, and then the electric signal istransmitted to the signal processing circuit 103. Then, the electricsignal is transmitted from the signal processing circuit 103 to thesecondary battery 104 in which the electric signal is stored as electricenergy.

The electric motor 111 drives the moving object 100 by converting theelectric energy stored in the secondary battery 104 into mechanicalenergy.

If the strength of the test signal is insufficient so that the chargingcannot be started, the positional relationship between the moving objectantenna circuit 102 and the power feeding device antenna circuit 201 ismodified by changing the position or direction of the moving object 100or the power feeding device 200. Alternatively, the positionalrelationship may be modified by directly changing the position ordirection of the moving object antenna circuit 102 or the power feedingdevice antenna circuit 201 without moving the moving object 100 or thepower feeding device 200. After modifying the positional relationship, atest signal is used to redetermine whether or not the positionalrelationship between the moving object antenna circuit 102 and the powerfeeding device antenna circuit 201 is in a state adapted to start of thecharging.

The strength of the radio wave transmitted as the test signal may besufficient as long as the positional relationship between the movingobject antenna circuit 102 and the power feeding device antenna circuit201 can be detected. Thus, the strength of the radio wave can besufficiently lower than that of the charging radio wave.

If test signals are transmitted plural times for the alignment, thestrengths of the test signals to be transmitted may not be necessarilyequal to each other. For example, the strength of a test signaltransmitted for alignment may be lowered for each alignment.Alternatively, if the positional relationship between the power feedingdevice antenna circuit 201 and the moving object antenna circuit 102 isunsuitable so that a test signal transmitted first cannot be received, atest signal with a strength higher than that of the first test signalmay be transmitted next.

In one embodiment of the present invention, the charging radio wave hasno limitation on its frequency and may have any band of frequency aslong as power can be transmitted. For example, the charging radio wavemay have any of an LF band of 135 kHz (long wave), a HF band of 13.56MHz, a UHF band of 900 MHz to 1 GHz, and a microwave band of 2.45 GHz.

In addition, the radio wave used as the test signal may have the samefrequency band as the charging radio wave or a frequency band differentfrom that of the charging radio wave.

A radio wave transmission method may be properly selected from variousmethods including an electromagnetic coupling method, an electromagneticinduction method, a resonance method, and a microwave method. In oneembodiment of the present invention, in order to prevent energy loss dueto foreign substances containing moisture, such as rain and mud, theelectromagnetic induction method or the resonance method using a lowfrequency band, more specifically, frequencies of a short wave of 3 MHzto 30 MHz, a medium wave of 300 kHz to 3 MHz, a long wave of 30 kHz to300 kHz, or a very-low frequency wave of 3 kHz to 30 kHz, may be used.

In one embodiment of the present invention, the data on the positionalrelationship between the moving object antenna circuit 102 and the powerfeeding device antenna circuit 201 may be extracted from the strength ofthe test signal. The data on the positional relationship helps thedriver of the moving object 100 to align the moving object 100 and thepower feeding device 200 while driving the moving object 100.Alternatively, this data helps the controller of operation of the powerfeeding device 200 to align the moving object 100 and the power feedingdevice 200 while operating the power feeding device 200. Accordingly,the moving object 100 and the power feeding device 200 can be easilyaligned to prevent power loss which may be caused when the battery ischarged. In addition, the strength of a radio wave radiated to thesurroundings from the power feeding device 200 without being used forcharging can be low.

Embodiment 2

In this embodiment, more detailed configurations of the moving objectand the wireless power feeding system using the moving object and thepower feeding device according to one embodiment of the presentinvention will be described.

The configurations of the moving object and the wireless power feedingsystem using the moving object and the power feeding device according toone embodiment of the present invention are shown in a block diagram ofFIG. 2 by way of an example. As shown in FIG. 2, the moving object 100includes the power receiving device portion 101 and the power loadportion 110 as in FIG. 1.

The power receiving device portion 101 includes at least the movingobject antenna circuit 102, the signal processing circuit 103, thesecondary battery 104, a rectifier circuit 105, a modulation circuit 106and a power supply circuit 107.

The power load portion 110 includes at least the electric motor 111 anda driving portion 112 whose operation is controlled by the electricmotor 111.

In addition, the power feeding device 200 includes at least the powerfeeding device antenna circuit 201, the signal processing circuit 202, arectifier circuit 203, a modulation circuit 204, a demodulation circuit205 and an oscillator circuit 206.

Subsequently, operations of the moving object 100 and the power feedingdevice 200 shown in FIG. 2 will be described with reference to a flowchart shown in FIG. 3.

The operations of the moving object 100 and the power feeding device 200shown in FIG. 2 may include a first stage of aligning the moving object100 and the power feeding device 200 and a second stage of performing acharging operation, as will be described below.

First, in the first stage, an alignment radio wave as a test signal istransmitted from the power feeding device antenna circuit 201 (A01:transmission of a test signal). Specifically, the signal processingcircuit 202 generates a signal required for alignment. This signalcontains data on the strength, the frequency, and the like of the radiowave. In accordance with this signal and a signal having a certainfrequency generated in the oscillator circuit 206, the modulationcircuit 204 applies a voltage to the power feeding device antennacircuit 201, whereby the alignment radio wave is transmitted, as thetest signal, from the power feeding device antenna circuit 201.

The test signal transmitted from the power feeding device antennacircuit 201 is received by the moving object antenna circuit 102 of themoving object 100 (B01: reception of the test signal). The moving objectantenna circuit 102 converts the received test signal into an electricsignal which is then rectified in the rectifier circuit 105 and is thentransmitted to the signal processing circuit 103.

The strength of the received test signal depends on the positionalrelationship in distance, direction, or the like between the movingobject antenna circuit 102 and the power feeding device antenna circuit201. The signal processing circuit 103 extracts data on the positionalrelationship between the moving object antenna circuit 102 and the powerfeeding device antenna circuit 201, from data on the strength of thetest signal in the electric signal transmitted from the rectifiercircuit 105.

Then, the signal processing circuit 103 determines based on the strengthof the received test signal whether or not the positional relationshipbetween the moving object antenna circuit 102 and the power feedingdevice antenna circuit 201 is in a state adapted to start of charging(B02: determination of whether a state is adapted to start of charging).

If the strength of the received test signal is insufficient, it meansthat the efficiency of energy conversion in converting the radio waveinto the electric signal is low. Accordingly, the positionalrelationship between the moving object antenna circuit 102 and the powerfeeding device antenna circuit 201 is determined to be not in a stateadapted to start of the charging. When such determination is made, thepositional relationship between the moving object antenna circuit 102and the power feeding device antenna circuit 201 is modified by changingthe position or direction of the moving object 100 or the power feedingdevice 200 (B03: modification of the positional relationship betweenantenna circuits). Alternatively, the positional relationship may bemodified by directly changing the position or direction of the movingobject antenna circuit 102 or the power feeding device antenna circuit201 without moving the moving object 100 or the power feeding device200. After modifying the positional relationship, the steps from thestep A01 (transmission of a test signal) to the step B02 (determinationof whether a state is adapted to start of charging) are repeated for thealignment.

If the strength of the received test signal is sufficiently high, itmeans that an efficiency of energy conversion in converting the radiowave into the electric signal is sufficiently high. Accordingly, thepositional relationship between the moving object antenna circuit 102and the power feeding device antenna circuit 201 is determined to be ina state adapted to start of charging.

If the positional relationship is determined to be in a state adapted tostart of charging, it means that the alignment has been finished andpreparation for charging has been completed. Then, the signal processingcircuit 103 generates a signal for notifying the power feeding device200 of the completed preparation. When the modulation circuit 106applies a voltage to the moving object antenna circuit 102 in accordancewith the generated signal, the signal for notification of completedpreparation is transmitted from the moving object antenna circuit 102 bya radio wave (B04: transmission of a signal for notification ofcompleted preparation).

The signal for notification of the completed preparation is received bythe power feeding device antenna circuit 201 of the power feeding device200 by the radio wave (A02: reception of the signal for notification ofcompleted preparation). The power feeding device antenna circuit 201converts the received signal into an electric signal which is thenrectified in the rectifier circuit 203. The rectified signal isdemodulated in the demodulation circuit 205 and is then transmitted tothe signal processing circuit 202. When the signal processing circuit202 receives the signal for notification of the completed preparation(the demodulated signal), the operations of the moving object 100 andthe power feeding device 200 proceed from the first stage to the secondstage.

In the second stage, a charging radio wave is transmitted from the powerfeeding device antenna circuit 201 (A03: transmission of a chargingradio wave). Specifically, the signal processing circuit 202 generates asignal required for charging. This signal contains data on the strength,the frequency, and the like of the radio wave. In accordance with thissignal and a signal having a certain frequency generated in theoscillator circuit 206, the modulation circuit 204 applies a voltage tothe power feeding device antenna circuit 201, whereby the charging radiowave is transmitted from the power feeding device antenna circuit 201.

The charging radio wave transmitted from the power feeding deviceantenna circuit 201 is received by the moving object antenna circuit 102of the moving object 100. The moving object antenna circuit 102 convertsthe received charging radio wave into an electric signal which is thenrectified in the rectifier circuit 105 and is then transmitted to thesignal processing circuit 103. Then, the rectified electric signal istransmitted from the signal processing circuit 103 to the secondarybattery 104 in which the electric signal is stored as electric energy.

When charging of the secondary battery 104 has been completed (B05:completion of the charging), the signal processing circuit 103 generatesa signal for notifying the power feeding device 200 of the completedcharging. When the modulation circuit 106 applies an AC voltage to themoving object antenna circuit 102 in accordance with the generatedsignal, a signal for notification of the completed charging istransmitted from the moving object antenna signal 102 by a radio wave(B06: transmission of a signal for notification of completed charging).

The signal for notification of the completed charging is received by thepower feeding device antenna circuit 201 of the power feeding device 200by the radio wave (A04: reception of the signal for notification ofcompleted charging). The power feeding device antenna circuit 201converts the received signal into an electric signal which is thenrectified in the rectifier circuit 203. The rectified signal isdemodulated in the demodulation circuit 205 and is then transmitted tothe signal processing circuit 202. Upon receiving the signal fornotification of the completed charging (the demodulated signal), thesignal processing circuit 202 transmits a signal for stopping thetransmission of the radio wave to the oscillator circuit 206 and themodulation circuit 204 to stop the transmission of the charging radiowave (A05: stop of the transmission of a charging radio wave).

The electric energy stored in the secondary battery 104 is made into aconstant voltage in the power supply circuit 107, which is then suppliedto the electric motor 111. The electric motor 111 converts the suppliedelectric energy into mechanical energy to actuate the driving portion112.

Although in this embodiment the signal processing circuit 103 of themoving object 100 determines whether to start the charging of thesecondary battery 104 and a result of the determination is transmittedto the power feeding device 200 by a radio wave, the present inventionis not limited thereto. For example, the data on the positionalrelationship between the power feeding device 200 and the moving object100 may be, as it is, transmitted, as a radio wave signal, from themoving object 100 to the power feeding device 200 in which it may bethen be determined whether to start the charging of the secondarybattery 104. In this case, the positional relationship may be modifiedby movement of the power feeding device 200. Alternatively, a signal forrequesting modification of the positional relationship may be sent fromthe power feeding device 200 to the moving object 100 and the positionalrelationship may be modified by movement of the moving object 100. Inaddition, since there is no need to send a signal for notification ofcompleted preparation for charging from the moving object 100 to thepower feeding device 200, the operations of the moving object 100 andthe power feeding device 200 may proceed directly from the step B02(determination of whether a state is adapted to start of charging) tothe step A03 (transmission of a charging radio wave).

A modulation method used in the modulation circuit 106 or the modulationcircuit 204 may be properly selected from various methods includingamplitude modulation, frequency modulation, and phase modulation.

The modulation circuit 106 modulates a carrier (a carrier wave)transmitted from the power feeding device antenna circuit 201 byapplying an AC voltage to the moving object antenna circuit 102 inaccordance with the signal for notification of the completed preparationor the signal for notification of the completed charging, whereby thesignal is transmitted from the moving object 100 to the power feedingdevice 200.

In addition, in the first stage, in order to instruct the power feedingdevice 200 to transmit the test signal, an oscillator circuit may beprovided in the power receiving device portion 101 of the moving object100 and a start signal may be transmitted from the moving object 100. Inthis case, the oscillator circuit may be electrically connected to themodulation circuit 106. FIG. 4 is a flow chart showing the case wherethe start signal is transmitted from the moving object 100. In the flowchart shown in FIG. 4, the signal processing circuit 103 generates thestart signal. The start signal contains data on the strength, thefrequency, and the like of a radio wave. Then, the modulation circuit106 applies a voltage to the moving object antenna circuit 102 inaccordance with this start signal and a signal having a certainfrequency generated in the oscillator circuit so that the start signalis transmitted from the moving object antenna circuit 102 by a radiowave (B00: transmission of the start signal for instructing transmissionof the test signal).

Then, the start signal is received by the power feeding device antennacircuit 201 of the power feeding device 200 (A00: reception of the startsignal). The power feeding device antenna circuit 201 converts thereceived signal into an electric signal which is then rectified in therectifier circuit 203. The rectified signal is demodulated in thedemodulation circuit 205 and is then transmitted to the signalprocessing circuit 202.

Upon receiving the start signal, the signal processing circuit 202generates a signal required for alignment. This signal contains data onthe strength, the frequency, and the like of a radio wave. In accordancewith this signal and a signal having a certain frequency generated inthe oscillator circuit 206, the modulation circuit 204 applies a voltageto the power feeding device antenna circuit 201, whereby an alignmentradio wave is transmitted, as a test signal, from the power feedingdevice antenna circuit 201 (A01: transmission of a test signal). Stepsfollowing the step A01 (transmission of a test signal) are the same asthose in the flow chart of FIG. 3; thus, the above description can bereferred to.

In addition, the moving object 100 shown in FIG. 2 may include ademodulation circuit in the power receiving device portion 101.Configurations of the moving object and the wireless power feedingsystem using the moving object and the power feeding device in the casewhere the moving object 100 includes a demodulation circuit 108 areshown in a block diagram of FIG. 5 by way of an example. FIG. 5 isdifferent from FIG. 2 in that the moving object 100 includes thedemodulation circuit 108 in the power feeding device portion 101.

Operations of the moving object 100 and the power feeding device 200shown in FIG. 5 can be described according to the flow charts shown inFIG. 3 and FIG. 4, as in the case of FIG. 2. However, if theseoperations are performed in accordance with the flow chart shown in FIG.4, an oscillator circuit may be installed in the power receiving deviceportion 101 of the moving object 100 and may be electrically connectedto the modulation circuit 106. In addition, in FIG. 5, upon receiving atest signal by a radio wave (B01: reception of the test signal), themoving object antenna circuit 102 converts the received test signal intoan electric signal which is then rectified in the rectifier circuit 105and then demodulated in the demodulation circuit 108. Then, thedemodulated test signal is sent to the signal processing circuit 103.

If the strength of the demodulated test signal is insufficient, thesignal processing circuit 103 can not perform signal processing based onthe test signal. Accordingly, the operation can not proceed to the nextstep of generating a signal for notifying the power feeding device 200of the completed preparation. On the other hand, if the strength of thedemodulated test signal is sufficiently high, signal processing isperformed based on the test signal. Accordingly, the operation canproceed to the next step of generating a signal for notifying the powerfeeding device 200 of the completed preparation. That is, since whetherthe signal processing circuit 103 can perform signal processing dependson the strength of the demodulated test signal, it can be determinedbased on the strength of the demodulated test signal, whether or not thepositional relationship between the moving object antenna circuit 102and the power feeding device antenna circuit 201 is in a state adaptedto start of charging (B02: determination of whether a state is adaptedto start of charging).

If the positional relationship is determined to be not in a stateadapted to start of the charging, the positional relationship betweenthe moving object antenna circuit 102 and the power feeding deviceantenna circuit 201 is modified by changing the position or direction ofthe moving object 100 or the power feeding device 200 (B03: modificationof the positional relationship between antenna circuits). Alternatively,the positional relationship may be modified by directly changing theposition or direction of the moving object antenna circuit 102 or thepower feeding device antenna circuit 201 without moving the movingobject 100 or the power feeding device 200. After modifying thepositional relationship, the steps from the step A01 (transmission of atest signal) to the step B02 (determination of whether a state isadapted to start of charging) are repeated for the alignment.

If the positional relationship is determined to be in a state adapted tostart of charging, the signal processing circuit 103 generates a signalfor notifying the power feeding device 200 of completed preparation.Then, the modulation circuit 106 applies an AC voltage to the movingobject antenna circuit 102 in accordance with the generated signal sothat a signal for notification of completed preparation is transmittedfrom the moving object antenna circuit 102 by a radio wave (B04:transmission of a signal for notification of completed preparation).Steps following the step B04 (transmission of a signal for notificationof completed preparation) are the same as those in the flow charts ofFIG. 3 and FIG. 4; thus, the above description can be referred to.

However, in FIG. 5, a charging radio wave may be converted into anelectric signal in the moving object antenna circuit 102 and may betransmitted to the signal processing circuit 103 after being rectifiedin the rectifier circuit 105, without passing through the demodulationcircuit 108.

In addition, the moving object 100 shown in FIG. 2 may include acombustion engine for a prime motor, in addition to the electric motor111. Configurations of the moving object and the wireless power feedingsystem using the moving object and the power feeding device in the casewhere the moving object 100 includes a combustion engine are shown in ablock diagram of FIG. 6 by way of an example.

Operations of FIG. 6 can be described according to the flow charts shownin FIG. 3 and FIG. 4, as in the cases of FIG. 2 and FIG. 5. However, ifthese operations are performed in accordance with the flow chart shownin FIG. 4, an oscillator circuit may be installed in the power receivingdevice portion 101 of the moving object 100 and may be electricallyconnected to the modulation circuit 106.

FIG. 6 is different from FIG. 2 in that the moving object 100 includes acombustion engine 113 in the power load portion 110 and the electricmotor 111 and the combustion engine 113 function as a prime motor 114.The electric energy stored in the secondary battery 104 is made into aconstant voltage in the power supply circuit 107, which is then suppliedto the electric motor 111 and the combustion engine 113.

The electric motor 111 converts the supplied electric energy intomechanical energy to actuate the driving portion 112. In addition, as aspark plug is ignited by the supplied electric energy, the combustionengine 113 is started to actuate the driving portion 112.

In addition, the moving object 100 shown in FIG. 2 may include an outputdevice in the power load portion 110. Configurations of the movingobject and the wireless power feeding system using the moving object andthe power feeding device in the case where the moving object 100includes an output device 115 in the power load portion 110 are shown ina block diagram of FIG. 7 by way of an example.

FIG. 7 is different from FIG. 2 in that the moving object 100 includesthe output device 115 and an input device 116 in the power load portion110. The output device 115 is a device which outputs data extracted froma test signal in the signal processing circuit 103 and examples of theoutput device 115 include a display, a light, a speaker, and the like.The input device 116 is a device which inputs external data to themoving object 100 and examples of the input device 116 include a handle,a brake, an accelerator, and a switch.

Operations of FIG. 7 can be described according to the flow charts shownin FIG. 3 and FIG. 4, as in the cases of FIG. 2, FIG. 5, and FIG. 6.However, if the operations are performed in accordance with the flowchart shown in FIG. 4, an oscillator circuit may be installed in thepower receiving device portion 101 of the moving object 100 and may beelectrically connected to the modulation circuit 106.

If it has been determined in the flow chart shown in FIG. 3 or FIG. 4whether or not the positional relationship between the moving objectantenna circuit 102 and the power feeding device antenna circuit 201 isin a state adapted to start of charging (B02: determination of whetherthe positional relationship is in a state adapted to start of charging),data on the determination result can be output using the output device115. Alternatively, data on relative strength of a test signal receivedby the moving object 100 may be output using the output device 115 andthe determination of whether the positional relationship is in a stateadapted to start of charging may be made by a driver.

A driver of the moving object 100 may use the data output using theoutput device 115 to determine the positional relationship between themoving object 100 and the power feeding device 200 or whether or notthere is a need to modify the positional relationship.

If there is a need to modify the positional relationship, the driver ofthe moving object 100 inputs data to be used to modify the position ordirection of the moving object 100 to the moving object 100 from theinput device 116. Then, the operation of the driving portion 112 iscontrolled based on the data input from the input device 116, wherebythe position or direction of the moving object 100 or the moving objectantenna circuit 102 is modified.

If there is no need to modify the positional relationship, data on aninstruction to proceed to the next step can be input to the movingobject 100 from the input device 116.

In addition, the output device 115 may output the data on how far theoperation proceeds in a series of steps from the initiation of alignmentto the completion of power transmission to the moving object 100.

In addition, in the block diagrams shown in FIG. 2, FIG. 5, FIG. 6, andFIG. 7, a DC-DC converter or an overcharging control circuit forcontrolling the operation of the power supply circuit 107 so as toprevent overcharging of the secondary battery 104 may be properlyinstalled.

In one embodiment of the present invention, the data on the positionalrelationship between the moving object antenna circuit 102 and the powerfeeding device antenna circuit 201 can be extracted from the strength ofthe test signal. In addition, the data on the positional relationshipassists in the alignment of the moving object 100 and the power feedingdevice 200 while the driver of the moving object 100 is driving themoving object 100. Alternatively, the data on the positionalrelationship assists in the alignment of the moving object 100 and thepower feeding device 200 while a controller of operation of the powerfeeding device 200 is operating the power feeding device 200.Accordingly, the moving object 100 and the power feeding device 200 canbe easily aligned to reduce power loss which may be caused when thebattery is charged. In addition, the strength of a radio wave radiatedto the surroundings from the power feeding device 200 without being usedfor the charging can be low.

This embodiment can be implemented in proper combination with any of theother embodiments.

Embodiment 3

In this embodiment, the positional relationship between a moving objectantenna circuit of a moving object and a power feeding device antennacircuit of a power feeding device will be described.

FIG. 8A shows a state where a four-wheeled automobile 300 as one ofmoving objects approaches a power feeding device antenna circuit 301 ofthe power feeding device. The automobile 300 approaches the powerfeeding device antenna circuit 301 in a direction indicated by an arrow.

The automobile 300 includes a moving object antenna circuit 302 providedon its bottom portion. In order to clearly show the position of themoving object antenna circuit 302 in the automobile 300, FIG. 8B showsthe outline of the automobile 300 and the moving object antenna circuit302 provided on the bottom portion of the automobile 300.

As the automobile 300 moves in the direction of the arrow, the movingobject antenna circuit 302 provided on the bottom portion of theautomobile 300 finally becomes adjacent to the power feeding deviceantenna circuit 301, as shown in FIG. 8C.

It may be difficult for a driver of the automobile 300 to exactly detectthe positional relationship between the antenna circuits from a driver'sseat of the automobile 300 and align the antenna circuits to secure highefficiency conversion, although it depends on where the power feedingdevice antenna circuit 301 and the moving object antenna circuit 302 areinstalled. However, in one embodiment of the present invention, since atest signal transmitted from and received by the antenna circuits isused to detect the positional relationship without direct perception ofthe antenna circuits with the eye, the alignment can be easily achieved.

In addition, as in this embodiment, if the moving object antenna circuit302 is provided on the bottom portion of the automobile 300 and thepower feeding device antenna circuit 301 is placed on a surface of aroad or the like on which the automobile 300 moves, a certain intervalis always between the antenna circuits. Accordingly, the alignment ofthe antenna circuits may be achieved by moving the power feeding deviceantenna circuit 301 in the surface (e.g. a road) on which the automobile300 moves. Alternatively, this may be achieved by moving the movingobject antenna circuit 302 in a surface (e.g. the bottom surface of theautomobile) parallel to the surface on which the automobile 300 moves.

In addition, although an efficiency of conversion of energy of a radiowave into electric energy depends greatly on a positional relationshipin distance, direction, or the like between the power feeding deviceantenna circuit 301 and the moving object antenna circuit 302, thedirections of the antenna circuits are fixed in FIGS. 8A to 8C.Accordingly, in FIGS. 8A to 8C, the power feeding device antenna circuit301 and the moving object antenna circuit 302 are only necessary to bealigned so that the distance between the antenna circuits is decreased.

FIG. 9A shows the state where a power feeding device antenna 303 of thepower feeding device antenna circuit 301 is adjacent to a moving objectantenna 304 of the moving object antenna circuit 302. It is assumed inFIG. 9A that a test signal is transmitted, as a radio wave, from thepower feeding device antenna 303.

It is preferable that the moving object antenna 304 is within an optimalarea 305 so that radio wave transmitted from the power feeding deviceantenna 303 is received with high efficiency. Since the conversionefficiency increases when the moving object antenna 304 is within theoptimal area 305, the moving object antenna 304 can receive a testsignal having high strength. On the contrary, if the moving objectantenna 304 is outside the optimal area 305 as shown in FIG. 9A, theconversion efficiency is low; thus, the moving object antenna 304 cannot receive a test signal having high strength.

FIG. 9B shows the state where the moving object antenna 304 is withinthe optimal area 305. It is assumed in FIG. 9B that a charging radiowave is transmitted from the power feeding device antenna 303.

As shown in FIG. 9B, since the conversion efficiency is high when themoving object antenna 304 is within the optimal area 305, it is possibleto prevent power loss which may be caused when the battery is charged.

A range of the optimal area 305 may be properly set by a designer. Forexample, in the case where a radio wave is transmitted/received using anelectromagnetic coupling method, when an alternating current (AC) flowsin the power feeding device antenna 303, the power feeding deviceantenna 303 is electromagnetically coupled to the moving object antenna304, which produces an induced electromotive force in the moving objectantenna 304. Accordingly, if an area in which a magnetic flux generatedin the power feeding device antenna 303 is most concentrated is set asthe optimal area 305, the induced electromotive force generated in themoving object antenna 304 can greatly increases, thereby increasing theconversion efficiency.

This embodiment can be implemented in proper combination with any of theother embodiments.

Embodiment 4

In this embodiment, a configuration of a moving object antenna circuitand a power feeding device antenna circuit will be described.

Each of a moving object antenna circuit and a power feeding deviceantenna circuit may be constituted by an LC circuit including an antennaand a capacitor. FIG. 10A shows a circuit diagram of an antenna circuitby way of an example.

As the antenna circuit shown in FIG. 10A, a parallel LC circuitincluding an antenna 401 and a capacitor 402 is used. Specifically, apair of terminals of the antenna 401 is respectively connected to aninput terminal 403 and an input terminal 404 of the antenna circuit. Inaddition, a pair of electrodes of the capacitor 402 is respectivelyconnected to the input terminal 403 and the input terminal 404 of theantenna circuit.

An AC voltage is applied between the input terminal 403 and the inputterminal 404 of the antenna circuit. In addition, the input terminal 404is connected to a node given a fixed potential such as a groundpotential.

As used herein, the term “connection” means electric connection andcorresponds to a state where a current, a voltage, or a potential can besupplied or transmitted. Accordingly, a connection state does notnecessarily indicate a direct connection state and may include anindirect connection state via a circuit element such as a wiring, adiode, or a transistor, in which supply or transmission of a current, avoltage, or a potential is possible.

In addition, as an antenna circuit shown in FIG. 10B, a serial LCcircuit including an antenna 401 and a capacitor 402 is used.Specifically, one of a pair of electrodes of the capacitor 402 isconnected to one of electrodes of the antenna 401, while the other isconnected to the input terminal 403 of the antenna circuit. In addition,the other electrode of the antenna 401 is connected to the inputterminal 404 of the antenna circuit.

An AC voltage is applied between the input terminal 403 and the inputterminal 404 of the antenna circuit. In addition, the input terminal 404is connected to a node given a fixed potential such as a groundpotential.

Although it is illustrated in FIGS. 10A and 10B that the antenna 401 hasthe shape of a coil, the shape of an antenna usable in the presentinvention is not limited thereto. The shape of the antenna 401 may beone which can transmit/receive a signal by wireless communication andmay be properly selected according to the wavelength and transmissionmethod of a radio wave.

For example, for transmission/reception of a signal using a microwavemethod, the antenna circuit may use impedance matching with a circuitportion to prevent power loss due to reflection, thereby increasing theefficiency of power transmission. Reactance corresponding to animaginary part of the impedance depends on capacitance of the capacitorof the antenna circuit. Accordingly, in order to increase the powertransmission efficiency, it is preferable to match impedances byoptimizing the capacitance of the capacitor.

For transmission/reception of a signal using an electromagneticinduction method, the power transmission efficiency can be increased byoptimizing the capacitance of the capacitor included in the antennacircuit.

FIGS. 11A to 11C illustrate examples of shapes of antennas. The antennashown in FIG. 11A has a rectangular flat plate with an opening formedtherein. The antenna shown in FIG. 11B has a spiral-shaped conductor410. The antenna shown in FIG. 11C has plate-shaped patch elements 411and 412 with a ring-shaped wiring 413 therebetween.

In addition to a coil connected to a feeder line at a power feedingpoint, the antenna circuit may have a radio wave transmission/receptioncoil which is not physically connected to the feeder line, like abooster antenna. A communication distance can be extended using theabove-described configuration.

This embodiment can be implemented in proper combination with any of theother embodiments.

Embodiment 5

In this embodiment, a configuration of a power feeding device which canfacilitate alignment in the case of using a moving object, such as anautomobile, which moves not on a rail, will be described.

FIG. 12A shows a state where a four-wheeled automobile 500 as one typeof moving object approaches a power feeding device antenna circuit 501of the power feeding device. The automobile 500 approaches the powerfeeding device antenna circuit 501 in a direction indicated by an arrow.

The automobile 500 has a driving wheel 504 which is included in adriving portion and is actuated using mechanical energy from an electricmotor. As the driving wheel 504 is rotated, the automobile 500 can bedriven. In this embodiment, as shown in FIG. 12A, in order to restrict adirection in which the automobile is driven, a guide 503 to fix adirection of a shaft of the driving wheel 504 is installed in the powerfeeding device. Accordingly, the driving wheel 504 rotates and movesalong a direction in which the guide 503 extends.

The automobile 500 has a moving object antenna circuit 502 provided onits bottom portion. As the automobile 500 moves in the arrow direction,the moving object antenna circuit 502 provided on the bottom portion ofthe automobile 500 is finally positioned adjacent to the power feedingdevice antenna circuit 501, as shown in FIG. 12B.

As in this embodiment, by using the guide 503, it is only necessary toalign the power feeding device antenna circuit 501 and the moving objectantenna circuit 502 in the direction in which the guide 503 extends.This can facilitate alignment further.

This embodiment can be implemented in proper combination with any of theother embodiments.

Embodiment 6

In one embodiment of the present invention, examples of moving objectsinclude moving means driven by an electric motor using power stored in asecondary battery, such as automobiles (automatic two-wheeled cars,three or more-wheeled automobiles), motorized bicycles including amotor-assisted bicycle, aircrafts, boats, and railroad cars.

FIG. 13A shows a configuration of a motor boat 1301 as one of the movingobjects of the present invention. FIG. 13A illustrates the case wherethe motor boat 1301 includes a moving object antenna circuit 1302equipped on a side of the body of the boat. For example, a power feedingdevice for charging the motor boat 1301 may be equipped at a mooring ina harbor. In addition, by equipping a power feeding device antennacircuit 1303 at a dike such as a quay in the mooring, it is possible tocharge the motor boat 1301 with power loss suppressed while the motorboat 1301 is anchored. If the charging can be achieved by wirelesscommunication, the trouble of removing a secondary battery from themotor boat 1301 for every charging can be saved.

FIG. 13B shows a configuration of an electric wheelchair 1311 as one ofthe moving objects of the present invention. FIG. 13B illustrates thecase where the electric wheelchair 1311 includes a moving object antennacircuit 1312 provided on its bottom portion. A power feeding deviceantenna circuit 1313 of a power feeding device for charging the electricwheelchair 1311 may be installed on a surface of a road or the like onwhich the electric wheelchair 1311 lies. It is possible to charge theelectric wheelchair 1311 with power loss suppressed when the electricwheelchair stops. If the charging can be achieved by wirelesscommunication, the trouble of removing a secondary battery from theelectric wheelchair 1311 for every charging can be saved. In addition,since strength of a radio wave radiated to the surroundings from thepower feeding device without being used for charging can be low, thepossibility that a user's health would be damaged due to leaked radiowaves can be reduced even when the user charges electric wheelchair 1311while sitting on the electric wheelchair 1311.

This embodiment can be implemented in proper combination with any of theother embodiments.

Embodiment 7

In this embodiment, a configuration of a rectifier circuit used in amoving object and configurations of transistors included in variouscircuits of the moving object will be described.

FIG. 14A shows an example of a half-wave rectifier circuit as one typeof rectifier circuit. The rectifier circuit shown in FIG. 14A includes atransistor 800 and a capacitor 803. One of a source electrode and adrain electrode of the transistor 800 is connected to an input terminal801, while the other is connected to an output terminal 802. A gateelectrode of the transistor 800 is connected to the input terminal 801.One of a pair of electrodes of the capacitor 803 is connected to theoutput terminal 802, while the other is connected to the ground (GND).

FIG. 14B shows an example of a half-wave voltage-doubler rectifiercircuit as one type of rectifier circuit. The rectifier circuit shown inFIG. 14B includes a transistor 810, a transistor 814, and a capacitor813. One of a source electrode and a drain electrode of the transistor810 is connected to an input terminal 811, while the other is connectedto an output terminal 812. A gate electrode of the transistor 810 isconnected to the input terminal 811. One of a source electrode and adrain electrode of the transistor 814 is connected to the input terminal811, while the other is connected to the ground (GND). A gate electrodeof the transistor 814 is connected to the ground (GND). One of a pair ofelectrodes of the capacitor 813 is connected to the output terminal 812,while the other is connected to the ground (GND).

The rectifier circuit of the moving object is not limited to theconfigurations shown in FIGS. 14A and 14B. For example, instead of thehalf-wave voltage-doubler rectifier circuit, any of the other half-waverectifier circuits such as a half-wave voltage-quadrupler rectifiercircuit or a half-wave voltage-sixtupler rectifier circuit, and afull-wave rectifier circuit may be used.

In addition, although it is illustrated that separate elements areconnected to each other in the circuit diagrams, in reality, oneconductive film may have functions of a plurality of elements, such as aportion of a wiring functioning as an electrode. As used herein, theterm “connection” includes the case where one conductive film hasfunctions of a plurality of elements.

In addition, a source electrode and a drain electrode of a transistormay be interchangeably referred to depending on polarity of thetransistor and a difference between potentials given to electrodes. Ingeneral, in an n-channel transistor, an electrode with a low potentialis called a source electrode, whereas an electrode with a high potentialis called a drain electrode. In a p-channel transistor, an electrodewith a low potential is called a drain electrode, whereas an electrodewith a high potential is called a source electrode. In thisspecification, although the connection relationship of the transistor issometimes described under the assumption that a source electrode and adrain electrode are fixed for the sake of convenience, in reality, thesource electrode and the drain electrode may be interchangeably referredto depending on the potential relationship.

Next, a configuration of a transistor used in a rectifier circuit, apower supply circuit, a signal processing circuit, a modulation circuit,a demodulation circuit, a selection circuit, and the like will bedescribed. In one embodiment of the present invention, a configurationof a transistor used in any of the above-mentioned circuits is notparticularly limited, but a transistor which can control a highwithstanding voltage and a high current is desirably used. In addition,if a range of temperatures under environments where the moving object isused is wide, a transistor whose characteristics change very littledepending on temperature is desirably used.

An example of a transistor which meets the requirement described abovemay include a transistor which uses, as semiconductor material, acompound semiconductor such as silicon carbide (SiC) or gallium nitride(GaN), or an oxide semiconductor formed of metal oxide such as zincoxide (ZnO), both of which have a wider band gap than a siliconsemiconductor and a lower intrinsic carrier density than silicon. Amongthem, the oxide semiconductor has the advantage that it can befabricated using a sputtering method or a wet method (a printing methodor the like) and has good mass productivity. While silicon carbide andgallium nitride can not have sufficient characteristics unless they aremonocrystalline and process temperatures for monocrystallization ofsilicon carbide and gallium nitride are about 1500° C. and about 1100°C., respectively, a film forming temperature of the oxide semiconductoris low, for example, 300° C. to 500° C. (about 700° C. at a maximum) anda semiconductor element including the oxide semiconductor can be stackedon an integrated circuit including a semiconductor material such assingle crystal silicon. In addition, larger substrates can be used.Accordingly, among the above-mentioned wide gap semiconductors, theoxide semiconductor has the advantage of being able to be mass produced.In addition, a crystalline oxide semiconductor having better performance(for example, field effect mobility) can be easily obtained by thermaltreatment at 450° C. to 800° C.

A highly purified oxide semiconductor (OS) with reduced impurities suchas moisture and hydrogen as electron donors (donors) is an i-typesemiconductor (an intrinsic semiconductor) or a substantially i-typesemiconductor. Thus, a transistor including the oxide semiconductor hasa characteristic of very low off-state current or leak current.Specifically, the highly purified oxide semiconductor has hydrogenconcentration of 5×10¹⁹/cm³ or less, preferably 5×10¹⁸/cm³ or less, morepreferably 5×10¹⁷/cm³ or less, still more preferably 1×10¹⁶/cm³ or less,when measurement of the hydrogen concentration is performed usingsecondary ion mass spectrometry (SIMS). In addition, the carrier densityof the oxide semiconductor which can be measured by Hall effectmeasurement is less than 1×10¹⁴/cm³, preferably less than 1×10¹²/cm³,more preferably less than 1×10¹¹/cm³. In addition, the band gap of theoxide semiconductor is 2 eV or more, preferably 2.5 eV or more, morepreferably 3 eV or more. By using a highly purified oxide semiconductorfilm with sufficiently reduced concentration of impurities such asmoisture and hydrogen, off-state current or leak current of thetransistor can be reduced.

Here, an analysis on the hydrogen concentration of the oxidesemiconductor film will be mentioned. Measurements of the hydrogenconcentration of the oxide semiconductor film and the hydrogenconcentration of the conductive film are performed by SIMS. Inprinciple, it is known that it is hard to obtain precise data on thevicinity of a sample surface or the vicinity of an interface with a filmincluding a different material by SIMS. Therefore, when a distributionof hydrogen concentrations of the film in its thickness direction isanalyzed by SIMS, an average value in a region in which values do notextremely vary and are substantially the same in a range where thetarget film exists is employed as the hydrogen concentration. Inaddition, if the thickness of the film is small, a region in whichsubstantially the same values are obtained cannot be found in some casesbecause the film is influenced by the hydrogen concentration of anadjacent film. In this case, the maximum or minimum of the concentrationof hydrogen in the region in which the film exists is employed as thehydrogen concentration of the film. In addition, if there is nomountain-like peak having a maximum value and no valley-like peak havinga minimum value in the region in which the film exists, a value at aninflection point is employed as the hydrogen concentration.

Specifically, it can be proved by various experiments that a transistorincluding a highly purified oxide semiconductor film as an active layerhas low off-state current. For example, even an element having a channelwidth of 1×10⁶ μm and a channel length of 10 μm can have thecharacteristic of having an off-state current (a drain current in thecase where a voltage between a gate electrode and a source electrode is0 V or less) of the measurement limit or less of a semiconductorparameter analyzer, i.e., 1×10⁻¹³ A or less, in a range of 1 V to 10 Vof a voltage between the source electrode and the drain electrode (adrain voltage). In this case, it can be seen that the off-state currentdensity corresponding to a value obtained by dividing the off-statecurrent by the channel width of the transistor is 100 zA/μm or less. Inaddition, in an experiment using a circuit where a capacitor isconnected to a transistor (the thickness of a gate insulating film is100 nm) and charges flowing in or out of the capacitor are controlled bythe transistor, when a highly purified oxide semiconductor film is usedfor a channel formation region of the transistor, a measurement of theoff-state current density of the transistor from variation of charges ofthe capacitor per unit time is 10 zA/μm to 100 zA/μm, which is furtherlow, in the case where the voltage between the source electrode and thedrain electrode of the transistor is 3 V. Accordingly, the off-statecurrent density of the transistor including the highly purified oxidesemiconductor film as an active layer can be 100 zA/μm or less,preferably 10 zA/μm or less, more preferably 1 zA/μm or less dependingon the voltage between the source electrode and the drain electrode.Accordingly, a transistor including the highly purified oxidesemiconductor film as an active layer has even lower off-state currentthan a transistor including crystalline silicon.

A transistor including the above-described oxide semiconductor for achannel formation region is desirably used for an element required tohave the characteristic of low off-state current, such as a switchingelement of a modulation circuit.

The off-state current of a transistor including a highly purified oxidesemiconductor hardly depends on temperature. This is because the oxidesemiconductor is made to be as close to intrinsic as possible byremoving impurities as electron donors (donors) in the oxidesemiconductor to highly purify the oxide semiconductor, so that theFermi level is located in a center of the forbidden band. In addition,this is because an energy gap of the oxide semiconductor is 3 eV or moreand there are very few thermally-excited carriers. In addition,degeneration of the source electrode and the drain electrode is also acause of no temperature dependence. The transistor is mostly operated bycarriers injected into the oxide semiconductor from the degeneratedsource electrode and the carrier density has no dependence ontemperature; therefore, the off-state current has no dependence ontemperature.

Examples of the oxide semiconductor include a quaternary metal oxidesuch as an In—Sn—Ga—Zn—O-based oxide semiconductor; ternary metal oxidessuch as an In—Ga—Zn—O-based oxide semiconductor, an In—Sn—Zn—O-basedoxide semiconductor, an In—Al—Zn—O-based oxide semiconductor, anSn—Ga—Zn—O-based oxide semiconductor, an Al—Ga—Zn—O-based oxidesemiconductor, and an Sn—Al—Zn—O-based oxide semiconductor; binary metaloxides such as an In—Zn—O-based oxide semiconductor, an Sn—Zn—O-basedoxide semiconductor, an Al—Zn—O-based oxide semiconductor, aZn—Mg—O-based oxide semiconductor, an Sn—Mg—O-based oxide semiconductor,an In—Mg—O-based oxide semiconductor, and an In—Ga—O-based oxidesemiconductor; an In—O-based oxide semiconductor; an Sn—O-based oxidesemiconductor; and a Zn—O-based oxide semiconductor. In thisspecification, the term “In—Sn—Ga—Zn—O-based oxide semiconductor” meansmetal oxide containing Indium (In), tin (Sn), gallium (Ga), and zinc(Zn) and may have any stoichiometric composition. In addition, the oxidesemiconductor may contain silicon.

The oxide semiconductor may be expressed by a chemical formula,InMO₃(ZnO)_(m) (m>0). Here, M represents one or more metal elementsselected from Ga, Al, Mn, and Co.

FIGS. 15A to 15D each show a structure of a transistor including anoxide semiconductor, which is formed over transistors including silicon.The silicon used may be either silicon included in a thin semiconductorfilm or silicon included in a bulk semiconductor substrate. In thisembodiment, a structure in the case where a transistor including anoxide semiconductor is formed over transistors formed using asilicon-on-insulator (SOI) substrate will be described by way of anexample.

FIG. 15A shows a transistor 601 and a transistor 602 which are formedusing an SOI substrate. In addition, a channel-etched bottom-gatetransistor 610 including an oxide semiconductor film is formed over thetransistor 601 and the transistor 602.

The transistor 610 includes a gate electrode 611, a gate insulating film612 over the gate electrode 611, an oxide semiconductor film 613 whichis over the gate insulating film 612 and overlaps with the gateelectrode 611, and a source electrode 614 and a drain electrode 615which are a pair and formed over the oxide semiconductor film 613. Inaddition, the transistor 610 may further include an insulating film 616formed over the oxide semiconductor film 613 as its component. Thetransistor 610 has a channel-etched structure where a portion of theoxide semiconductor film 613 is exposed between the source electrode 614and the drain electrode 615.

In addition, the transistor 610 may further include a back gateelectrode over the insulating film 616. The back gate electrode isformed to overlap with a channel formation region of the oxidesemiconductor film 613. The back gate electrode may be in either afloating state where the electrode is electrically isolated, or a statewhere the electrode is given a potential. In the latter, the back gateelectrode may be given the same potential as the gate electrode 611 or afixed potential such as a ground potential. By controlling the potentialsupplied to the back gate electrode, it is possible to set the thresholdvoltage of the transistor 610.

FIG. 15B shows the transistor 601 and the transistor 602 which areformed using an SOI substrate. In addition, a channel-protectivebottom-gate transistor 620 including an oxide semiconductor film isformed over the transistor 601 and the transistor 602.

The transistor 620 includes a gate electrode 631, a gate insulating film632 over the gate electrode 631, an oxide semiconductor film 633 whichis over the gate insulating film 632 and overlaps with the gateelectrode 631, a channel protective film 634 which is formed over theisland-like oxide semiconductor film 633 at a position overlapping withthe gate electrode 631, and a source electrode 635 and drain electrode636 which are formed over the oxide semiconductor film 633. In addition,the transistor 620 may further include an insulating film 637 formedover the source electrode 635 and drain electrode 636 as its component.

The channel protective film 634 is provided to prevent damage (forexample, thickness reduction due to plasma or an etchant in etching) ofa portion of the oxide semiconductor film 633, which is to be a channelformation region, in a later step. This can improve reliability of thetransistor.

By using an oxygen-containing inorganic material for the channelprotective film 634, even if oxygen vacancy in the oxide semiconductorfilm 633 occurs due to heat treatment for reduction of moisture andhydrogen, oxygen can be supplied to a region of the oxide semiconductorfilm 633, which is in contact with at least the channel protective film634, thereby reducing the oxygen vacancy as a donor to obtain astructure which satisfies the stoichiometric composition. Thus, thechannel formation region can be made to be i-type or substantiallyi-type and variation of electric characteristics of the transistor dueto oxygen vacancy can be reduced, which result in improvement of theelectric characteristics.

In addition, the transistor 620 may further include a back gateelectrode over the insulating film 637. The back gate electrode isformed to overlap with a channel formation region of the oxidesemiconductor film 633. The back gate electrode may be in either afloating state where the electrode is electrically isolated, or a statewhere the electrode is given a potential. In the latter, the back gateelectrode may be given the same potential as the gate electrode 631 or afixed potential such as a ground potential. By controlling the potentialsupplied to the back gate electrode, it is possible to set the thresholdvoltage of the transistor 620.

FIG. 15C shows the transistor 601 and the transistor 602 which areformed using an SOI substrate. In addition, a bottom-contact transistor640 including an oxide semiconductor film is formed over the transistor601 and the transistor 602.

The transistor 640 includes a gate electrode 641, a gate insulating film642 over the gate electrode 641, a source electrode 643 and a drainelectrode 644 which are over the gate insulating film 642, and an oxidesemiconductor film 645 which overlaps with the gate electrode 641. Inaddition, the transistor 640 may further include an insulating film 646formed on the oxide semiconductor film 645 as its component.

In addition, the transistor 640 may further include a back gateelectrode over the insulating film 646. The back gate electrode isformed to overlap with a channel formation region of the oxidesemiconductor film 645. The back gate electrode may be in either afloating state where the electrode is electrically isolated, or a statewhere the electrode is given a potential. In the latter, the back gateelectrode may be given the same potential as the gate electrode 641 or afixed potential such as a ground potential. By controlling the potentialsupplied to the back gate electrode, it is possible to set the thresholdvoltage of the transistor 640.

FIG. 15D shows the transistor 601 and the transistor 602 which areformed using an SOI substrate. In addition, a top-gate transistor 650including an oxide semiconductor film is formed over the transistor 601and the transistor 602.

The transistor 650 includes a source electrode 651 and a drain electrode652, an oxide semiconductor film 653 which is formed over the sourceelectrode 651 and the drain electrode 652, a gate insulating film 654over the oxide semiconductor film 653, and a gate electrode 655 which isover the gate insulating film 654 and overlaps with the oxidesemiconductor film 653. In addition, the transistor 650 may furtherinclude an insulating film 656 formed on the gate electrode 655 as itscomponent.

Although all of the above-described transistors have single-gatestructures in the drawings, they may have multi-gate structuresincluding a plurality of electrically connected gate electrodes, thatis, a plurality of channel formation regions.

This embodiment may be practiced in combination with other embodimentsdescribed above.

This application is based on Japanese Patent Application serial no.2010-023706 filed with Japan Patent Office on Feb. 5, 2010, the entirecontents of which are hereby incorporated by reference.

What is claimed is:
 1. A power receiving device comprising: an antennacircuit configured to generate a first electric signal and a secondelectric signal from a first radio wave and a second radio wavesequentially transmitted from a power feeding device, respectively; asignal processing circuit configured to extract data on a positionalrelationship between the antenna circuit and the power feeding device,using the first electric signal; a secondary battery configured to storeelectric energy using the second electric signal; an oscillator circuitconfigured to generate a signal having a certain frequency; and amodulation circuit configured to apply a voltage to the antenna circuitin accordance with a start signal and the signal having the certainfrequency, wherein the start signal is generated in the signalprocessing circuit.
 2. The power receiving device according to claim 1,wherein the antenna circuit comprises an antenna including a conductorthat has a spiral shape, and a capacitor.
 3. The power receiving deviceaccording to claim 1, wherein the antenna circuit is configured totransmit a third radio wave which is generated in accordance with thestart signal, to the power feeding device.
 4. The power receiving deviceaccording to claim 1, further comprising an output device configured tooutput the extracted data.
 5. A power receiving device comprising: anantenna circuit configured to generate a first electric signal and asecond electric signal from a first radio wave and a second radio wavesequentially transmitted from a power feeding device, respectively; arectifier circuit configured to rectify the first electric signal andthe second electric signal; a signal processing circuit configured toextract data on a positional relationship between the antenna circuitand the power feeding device, using the first electric signal which isrectified; a secondary battery configured to store electric energy usingthe second electric signal which is rectified; an oscillator circuitconfigured to generate a signal having a certain frequency; and amodulation circuit configured to apply a voltage to the antenna circuitin accordance with a start signal and the signal having the certainfrequency, wherein the start signal is generated in the signalprocessing circuit.
 6. The power receiving device according to claim 5,wherein the antenna circuit comprises an antenna including a conductorthat has a spiral shape, and a capacitor.
 7. The power receiving deviceaccording to claim 5, wherein the antenna circuit is configured totransmit a third radio wave which is generated in accordance with thestart signal, to the power feeding device.
 8. The power receiving deviceaccording to claim 5, further comprising an output device configured tooutput the extracted data.
 9. A power receiving device comprising: anantenna circuit configured to generate a first electric signal and asecond electric signal from a first radio wave and a second radio wavesequentially transmitted from a power feeding device, respectively; arectifier circuit configured to rectify the first electric signal andthe second electric signal; a signal processing circuit configured toextract data on a positional relationship between the antenna circuitand the power feeding device, using the first electric signal which isrectified; a secondary battery configured to store electric energy usingthe second electric signal which is rectified; an oscillator circuitconfigured to generate a signal having a certain frequency; and amodulation circuit configured to apply a voltage to the antenna circuitin accordance with a start signal and the signal having the certainfrequency, wherein the start signal is generated in the signalprocessing circuit, and wherein at least one of the rectifier circuit,the signal processing circuit and the modulation circuit comprises atransistor including an oxide semiconductor layer.
 10. The powerreceiving device according to claim 9, wherein the antenna circuitcomprises an antenna including a conductor that has a spiral shape, anda capacitor.
 11. The power receiving device according to claim 9,wherein the antenna circuit is configured to transmit a third radio wavewhich is generated in accordance with the start signal, to the powerfeeding device.
 12. The power receiving device according to claim 9,further comprising an output device configured to output the extracteddata.